Optical fiber coating composition and method of preparing a cured coating composition

ABSTRACT

A curing composition comprising (1) a fluorine-containing curing monomer containing a fluorinated alkyl group having not less than 6 carbon atoms, (2) a fluorine-containing curing monomer containing a fluorinated alkyl group having not more than 5 carbon atoms, and (3) a polyfunctional curing monomer, the weight ratio of said fluorine-containing curing monomer (1) to said fluorine-containing curing monomer (2) ranging from 75/25 to 99/1. The composition is coated on an optical fiber base and cured by active energy rays to provide a core/clad optical fiber excellent in transparency, mechanical strength, environmental resistance, and optical characteristics.

FIELD OF THE INVENTION

This invention relates to an optical fiber and a curing composition foroptical fiber cladding. More particularly, it relates to an opticalfiber excellent in mechanical strength, environmental resistance, andoptical characteristics and to a curing composition for producing thesame.

BACKGROUND OF THE INVENTION

Plastic-clad optical fibers comprising quartz, silica, glass, etc. as acore and plastics as a cladding (hereinafter abbreviated as PCF) arerelatively cheap, excellent in light transmission, and easy to have anincreased numerical aperture and are therefore used as optical fibersfor short-to-medium distance communication or light guides.

While silicone resins have conventionally been used as claddingmaterials, fluorine-containing resins having high hardness have recentlybeen proposed and practically used as cladding materials from thestandpoint of easy handling and environmental resistance as disclosed inU.S. Pat. Nos. 4,511,209 and 4,707,076, JP-A-63-40104, JP-A-63-43104,JP-A-63-208805, JP-A-63-208806, JP-A-63-208807,JP-A-63-249112, EP257863, and EP 333464 (the term “JP-A” as used herein means an“unexamined published Japanese patent application”) In particular, EP257863 discloses an active energy ray-curing cladding material mainlycomprising fluorinated acrylates and an optical fiber using thecomposition as a cladding material, in which the curable claddingmaterial comprises a fluorine-containing curing monomer containing afluorinated alkyl group having not less than 6 carbon atoms, afluorine-containing curing monomer containing a fluorinated alkyl grouphaving not more than 5 carbon atoms, and a polyfunctional curing monomerwith a weight ratio of the former fluorine-containing curing monomer tothe latter fluorine-containing curing monomer being 68/32.

However, having poor compatibility or homogeneity at room temperature,the above-described curable cladding material, when coated as such atroom temperature, provides optical fibers having seriously deterioratedoptical characteristics such as light transmission properties. Besides,the formed cladding has poor adhesion to the core and easily peels off,causing reduction of environmental resistance or tensile strength of theoptical fiber, eventually making the optical fiber useless. Where thecladding material is heated for coating so as to have improvedcompatibility or homogeneity, the heating temperature must be strictlycontrolled to prevent eccentricity, etc., which accordingly requires acomplicated drawing apparatus and deteriorates workability. Further,where the cladding resin is rendered transparent at room temperature,the resulting cladding layer would have reduced mechanical strength andan increased refractive index and fail to maintain a desired numericalaperture.

Therefore, under the present situation, there is no cladding materialwhich exhibits satisfactory transparency at room temperature, has a lowrefractive index and excellent workability, and exhibits excellenttransparency and dynamic strength after curing to thereby provide anoptical fiber having sufficient dynamic strength, opticalcharacteristics, and environmental resistance, e.g., heat- andhumidity-resistance.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a curingcomposition which provides a cured resin simultaneously satisfying therequirements of transparency, mechanical strength, environmentalresistance, and optical characteristics.

Another object of the present invention is to provide an optical fibersimultaneously satisfying the requirements of transparency, mechanicalstrength, environmental resistance, and optical characteristics.

As a result of extensive investigations, the inventors have now foundthat the above objects of the present invention are accomplished by acuring composition comprising at least two fluorine-containing curingmonomers different in carbon atom number of the fluorinated alkyl groupthereof at a specific mixing ratio, thus having reached the presentinvention.

The present invention provides a curing composition including (1) afluorine-containing curing monomer containing a fluorinated alkyl grouphaving not less than 6 carbon atoms (hereinafter simply referred to asmonomer (1)), (2) a fluorine-containing curing monomer containing afluorinated alkyl group having not more than 5 carbon atoms (hereinaftersimply referred to as monomer (2)), and (3) a polyfunctional curingmonomer (hereinafter simply referred to as monomer (3)), the weightratio of monomer (1) to monomer (2) ranging from 75/25 to 99/1.

The present invention also provides an optical fiber comprising anoptical fiber base and a coated and cured layer comprising theabove-described curing composition.

DETAILED DESCRIPTION OF THE INVENTION

The optical fiber base which can be used in the present invention may beany of commonly employed bases and includes, for example, optical fibercores made of quartz, silica, glass, or plastics and optical fibershaving a core/cladding structure.

Monomers (1) and (2) which can be used in the present invention can beselected from any known compounds having a polymerizable ethylenicallyunsaturated group. Monomers having the following acrylic ester groups oranalogous groups thereof are suitable from the viewpoint of availabilityand requirements for the particular use as a cladding material, that is,dynamic strength and optical characteristics.

Monomer (1) preferably includes fluorinated (meth)acrylates representedby formula (A):RfOCOC(R)═CH₂  (A)wherein Rf represents a fluorinated alkyl group having not less than 6carbon atoms, which may be either straight or branched or which maycontain in the main chain thereof an oxygen atom, e.g.,(CF₃)₂CFOC(CF₃)FCF₂—; and R represents a hydrogen atom, a methyl group,or a fluorine atom.

The terminology “(meth)acrylate” as used herein inclusively meanscompounds containing an acryloyl group, a methacryloyl group, or anα-fluorinated acryloyl group.

Specific examples of the fluorinated (meth)acrylate represented byformula (A) are shown below for illustrative purposes only but not forlimitation:

a-1: CH₂═CHCOOCH₂CH₂C₈F₁₇ a-2: CH₂═C(CH₃)COOCH₂CH₂C₈F₁₇ a-3:CH₂═CHCOOCH₂CH₂C₁₂F₂₅ a-4: CH₂═C(CH₃)COOCH₂CH₂C₁₂F₂₅ a-5:CH₂═CHCOOCH₂CH₂C₁₀F₂₁ a-6: CH₂═C(CH₃)COOCH₂C₁₀F₂₁ a-7:CH₂═CHCOOCH₂CH₂C₆F₁₃ a-8: CH₂═C(CH₃)COOCH₂CH₂C₆F₁₃ a-9:CH₂═CHCOOCH₂CH₂C₄F₉ a-10: CH₂═C(F)COOCH₂CH₂C₆F₁₃ a-11:CH₂═CHCOOCH₂(CH₂)₆CF(CF₃)₂ a-12: CH₂═CHCOOCH₂(CF₂)₆H a-13:CH₂═CHCOOCH₂(CF₂)₆H a-14: CH₂═C(CH₃)COOCH₂(CF₂)₈H a-15:CH₂═CHCOOCH₂(CF₂)₁₀H a-16: CH₂═CHCOOCH₂(CF₂)₁₂H a-17:CH₂═CHCOOCH₂C(OH)HCH₂C₈F₁₇ a-18: CH₂═CHCOOCH₂CH₂N(C₃H₇)SO₂C₈F₁₇ a-19:CH₂═CHCOOCH₂CH₂N(C₂H₅)COC₇F₁₅ a-20: CH₂═CHCOO(CH₂)₂(CF₂)₈CF(CF₃)₂ a-21:CH₂═C(CH₂CH₂C₈F₁₇)COOCH₂CH₂C₈F₁₇

The fluorinated (meth)acrylates (A) may be used either individually orin combinations of two or more thereof.

Preferred fluorinated (meth)acrylates (A) are those represented byformula (A-1) or (A-2):C₈F₁₇CH₂CH₂OCOC(R)═CH₂  (A-1)C₆F₁₇CH₂CH₂OCOC(R)═CH₂  (A-2)wherein R is as defined above.

Among the above-mentioned specific examples, preferred fluorinated(meth)acrylates (A) are a-1, a-2, a-7, and a-8, and particularly a-1 anda-7, from the standpoint of transparency, dynamic strength, and solventresistance of a cured resin and optical characteristics, dynamicstrength and solvent resistance of the optical fibers, especially PCF,prepared by using the curing composition.

Monomer (2) preferably includes fluorinated (meth)acrylates representedby formula (B):Rf′OCOC(R)═CH₂  (B)wherein Rf′ represents a fluorinated alkyl group containing not morethan 5 carbon atoms, which may be either straight or branched; and R isas defined above.

Specific examples of the fluorinated (meth)acrylates represented byformula (B) are shown below for illustrative purposes only but not forlimitation:

b-1: CH₂═CHCOOCH₂CF₃ b-2: CH₂═CHCOOCH₂CF₂CF₃ b-3: CH₂═CHCOOCH₂CFHCF₃b-4: CH₂═C(CH₃)COOCH₂CFHCF₃ b-5: CH₂═CHCOOCH₂CH₂CF₃ b-6:CH₂═CHCOOCH₂CF₂CFHCF₃ b-7: CH₂═CHCOOCH₂CF(CF₃)CF₃ b-8: CH₂═CHCOOCH(CF₃₂) b-9: CH₂═C(F)COOCH(CF₃ ₂) b-10: CH₂═C(CH₃)COOCH(CF₃)₂ b-11:CH₂═CHCOOCH₂(CF₂CF₂)₂H b-12: CH₂═C(F)COOCH₂(CF₂CF₂)₂H b-13:CH₂═C(CH₃)COOCH₂(CF₂CF₂)₂H b-14: CH₂═CHCOOCH₂CF₂CF₂CFHCF₃

The fluorinated (meth)acrylates (B) may be used either individually orin combinations of two or more thereof.

Preferred fluorinated (meth)acrylates (B) are those represented byformula (B-1) or (B-2):H(CF₂CF₂)₂CH₂OCOC(R)═CH₂  (B-1)(CF₃)₂CHOCOC(R)═CH₂  (B-2)wherein R is as defined above.

Among the above-mentioned specific examples, preferred fluorinated(meth)acrylates (B) are those in which the terminal fluorine atoms ofthe fluorinated alkyl group thereof are partly substituted with ahydrogen atom and those in which the fluorinated alkyl group thereof hasa branched structure from the standpoint of compatibility or homogeneityof the curing composition at room temperature; stability of theseproperties; workability and productivity in the production of opticalfibers (especially PCF); and optical characteristics and dynamicstrength of the optical fibers (especially PCF). Those having a branchedfluorinated alkyl group are particularly preferred from the viewpoint ofsolvent resistance of a cured resin.

To accomplish the objects of the present invention, it is essential tomix monomers (1) and (2). The monomers (1) to (2) mixing ratio rangesfrom 75/25 to 99/1 by weight, and preferably from 80/20 to 99/1 byweight. If the monomers (1) to (2) mixing ratio is out of theabove-mentioned range, compatibility and transparency at roomtemperature, stability of these properties, dynamic strength, andoptical characteristics of the curing composition are deteriorated.Further, such a curing composition has reduced workability or efficiencyin the production of optical fibers. Furthermore, the resulting opticalfibers undergo reductions in dynamic strength, optical characteristicsand environmental resistance such as solvent resistance.

Monomer (3) may be any of commonly employed polyfunctional curingmonomers. Particularly preferred are those generally calledpolyfunctional (meth)acrylates or special acrylates, and those generallycalled prepolymers, base resins, oligomers or acrylic oligomers(hereinafter inclusively referred to as (meth)acrylates (C)). Specificexamples of (meth)acrylates (C) are shown below.

-   -   (i) Polyfunctional (meth)acrylates containing two or more        (meth)acrylic ester groups bonded to a polyhydric alcohol.    -   (ii) Polyester acrylates containing two or more (meth)acrylic        ester groups bonded to a polyester polyol obtained by the        reaction between a polyhydric alcohol and a polybasic acid.

Examples of the polyhydric alcohols in (i) and (ii) above are ethyleneglycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, neopentylglycol, trimethylolpropane, dipropylene glycol, polyethylene glycol,polypropylene glycol, pentaerythritol, and dipentaerythritol. Examplesof the polybasic acids in (ii) are phthalic acid, adipic acid, maleicacid, trimellitic acid, itaconic acid, succinic acid, terephthalic acid,and an alkenylsuccinic acid.

-   -   (iii) Epoxy-modified (meth)acrylates comprising an epoxy resin        whose epoxy group is esterified with (meth)acrylic acid to a        (meth)acryloyl functional group.

Examples of the epoxy resin are bisphenol A-epi-chlorohydrin epoxyresins, phenol-novolak-epi-chlorohydrin epoxy resins, and polyhydricalcohol-epi-chlorohydrin alicyclic resins.

-   -   (iv) Polyurethane acrylates obtained by reacting a        polyisocyanate compound with a hydroxyl-containing        (meth)acrylate.

Examples of the polyisocyanate compound include compounds having apolyester, polyether or polyurethane skeleton having bonded to bothterminals of an isocyanate group.

-   -   (v) Polyether (meth)acrylates, melamine (meth)acrylates, alkyd        (meth)acrylates, isocyanurate (meth)acrylate, and silicone        (meth)acrylates.

Specific examples of (meth)acrylates (C) are shown below forillustrative purposes only but not for limitation.

c-1: Ethylene glycol di(meth)acrylate c-2: Diethylene glycoldi(meth)acrylate c-3: Triethylene glycol di(meth)acrylate c-4:Polyethylene glycol di(meth)acrylate (number average molecular weight:150-1000) c-5: Propylene glycol glycol di(meth)acrylate c-6: Dipropyleneglycol di(meth)acrylate c-7: Tripropylene glycol di(meth)acrylate c-8:Polypropylene glycol di(meth)acrylate (number average molecular weight:200-1000) c-9: Neopentyl glycol di(meth)acrylate c-10: 1,3-Butanediolglycol di(meth)acrylate c-11: 1,4-Butanediol glycol di(meth)acrylatec-12: 1,6-Hexanediol glycol di(meth)acrylate c-13: Hydroxypivalic esterneopentyl glycol di(meth)acrylate c-14: Bisphenol A glycoldi(meth)acrylate c-15: Trimethylolpropane tri(meth)acrylate c-16:Pentaerythritol tri(meth)acrylate c-17: Dipentaerythritolhexa(meth)acrylate c-18: Pentaerythritol tetra(meth)acrylate c-19:Trimethylolpropane di(meth)acrylate c-20: Dipentaerythritolmonohydroxypenta(meth)acrylate

These (meth)acrylates (C) are commercially available under the followingtrade names. The parentheses indicate the corresponding compound No.listed above.

-   Neomer MA-305 (c-21), Neomer BA-60 (c-22), Neomer TA-505 (c-23),    Neomer TA-401 (c-24), Neomer PHA 405X (c-25), Neomer TA 705X (c-26),    Neomer EA 400X (c-27).-   Neomer EE 401X (c-28), Neomer EP 405X (c-29), Neomer HB 601X (c-30),    and Neomer HB 605X (c-31) - all produced by Sanyo Chemical    Industries, Ltd.-   KAYARAD HY-220 (c-32), HX-620 (c-33), D-310 (c-34), D-320 (c-35),    D-330 (c-36), DPHA (c-37), DPCA-20 (c-38), DPCA-30 (c-39), DPCA-60    (c-40), and DPCA-120 (c-41) - all produced by Nippon Kayaku Co.,    Ltd.-   FA-713A (c-42) - produced by Hitachi Chemical Co., Ltd.

These polyfunctional (meth)acrylates (C) may be used either individuallyor in combinations of two or more thereof.

According to the inventors' finding, preferred of the above described(meth)acrylates (C) are c-9 and c-15, and particularly c-15, from thestandpoint of compatibility with fluorinated (meth)acrylates (A) and (B)and optical characteristics and dynamic strength after curing.

For the purpose of reducing a refractive index of the curingcomposition, fluorine-containing polyfunctional monomers, such as thoserepresented by formula shown below, may also be used as monomer (3).

 CH₂═C(R)COO(CH₂)_(x)(CF₂)_(y)(CH₂)_(x-)OOCC(R)═CH₂

wherein R is as defined above; x represents 1 or 2; and y represents aninteger of from 4 to 12.

Specific examples of such fluorine-containing polyfunctional monomersare shown below.

c-43: CH₂═CHCOOCH₂(C₂F₄)₂CH₂OCOCH═CH₂ c-44:CH₂═CHCOOC₂H₄(C₂F₄)₃C₂H₄OCOCH═CH₂ c-45:CH₂═C(CH₃)COOC₂H₄(C₂F₄)₃C₂H₄OCOC(CH₃)═CH₂ c-46:CH₂═C(F)COOC₂H₄(C₂F₄)₆C₂H₄OCOC(F)═CH₂ c-47:CH₂═CHCOOC₂H₄(C(CF₃)FCF₂)₄C₂H₄OCOCH═CH₂ c-48:CH₂═CHCOOC₂H₄(C₂H₄)₆(C(CF₃)FCF₂)₆ C₂H₄OCOCH═CH₂

The fluorine-containing polyfunctional monomer further includescompounds represented by formula:CH₂═C(R)COOCH₂C(OH)HCH₂Rf′OCH₂. C(OH)HCH₂OCOC(R)═CH₂wherein R is as defined above; and Rf′ represents(CH₂)_(x)(CF₂)_(y)(CH₂)_(x), wherein x and y are as defined above,

The proportion of monomer (3) in the curing composition is notparticularly limited but preferably ranges from 1 to 50% preferably from1 to 45%, and more preferably from 1 to 30%, by weight from theviewpoint of optical characteristics and dynamic strength.

As monomer (3), trimethylolpropane triacrylate is preferably used fromthe standpoint of compatibility with monomer (1) and monomer (2), curingproperty, and transparency, dynamic strength, and solvent resistanceafter curing, and further optical characteristics, mechanical strength,and solvent resistance as optical fibers.

In order to improve environmental resistance of the curing compositionafter curing, such as heat resistance and moisture resistance, and toimprove the same properties of the curing composition after molded intoa cladding layer, it is very effective to incorporate in the curingcomposition an antioxidant, such as thiol-containing compounds andhindered phenol compounds. From the standpoint of curing properties andenvironmental resistance of the composition, thiol-containing compoundsare preferred.

Thiol-containing compounds as antioxidant include monofunctional thiolcompounds, such as alkylthiol compounds having from 2 to 18 carbon atomsin the alkyl moiety thereof, thioglycolic esters containing an alkylgroup having from 2 to 18 carbon atoms, and C₈F₁₇CH₂CH₂SH; andpolyfunctional thiol compounds having at least two thiol groups permolecule, such as neopentyl thioglycol, trithiomethylolpropane, andthiodicarboxylic acid esters, e.g., dilauryl thiodipropionate.Particularly preferred of these thiol-containing compounds isγ-mercaptopropyltrimethoxysilane which contains a coupling group as wellas a thiol group per molecule and contributes to excellent environmentalresistance, i.e., heat- and moisture-resistance, of optical fibers,particularly PCF.

Specific examples of hindered phenol compounds useful as antioxidant are2,6-di-t-butyl-4-methylphenol,2,2′-methylenebis(4-methyl-6-t-butylphenol),4,4′-thiobis(6-t-butyl-3-methylphenol),4,4′butylidene-bis(3-methyl-6-t-butylphenol),1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)-benzene,1,3,5-tris(2-methyl-4-hydroxy-5-t-butylphenol)butane,octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, triethyleneglycol bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate],1,6-hexanediol bis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate],2,2-thio-diethylenebis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate],andpentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate].

These thiol-containing compounds and hindered phenol compounds may beused either individually or in combinations of two or more thereof.

The proportion of the thiol-containing compounds or hindered phenolcompounds in the curing composition ranges from 0.01 to 5% by weightand, for better optical characteristics and dynamic strength aftercuring, from 0.01 to 3% by weight.

If desired, the curing composition of the present invention may furthercontain other various additives and a photopolymerization initiator inaddition to the above-described components.

Additives which can be used in the present invention include polymersand solvents for viscosity adjustment; light stabilizers, coloringagents; coupling agents for improving adhesion between an optical fiberbase and a cladding; defoaming agents, leveling agents, and surfaceactive agents for uniform coating; surface modifiers for controllingadhesion between optical fibers and a primary coating; flame retardants;and plasticizers.

Useful coupling agents include silane coupling agents, titanium couplingagents, and zirco-aluminate coupling agents, with silane coupling agentsbeing preferred. Specific examples of the silane coupling agents aredimethyldimethoxysilane, dimethyldiethoxysilane, methyltrimethoxysilane,dimethylvinylmethoxysilane, phenyltrimethoxysilane,γ-chloropropyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane,γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane,γ-glycidoxypropylmethyldimethoxysilane,γ-methacryloxypropylmethoxysilane,γ-methacryloxypropylmethyldimethoxysilane,γ-acryloxypropylmethyltrimethoxysilane,γ-acryloxypropylmethyldimethoxysilane, andγ-mercaptopropyltrimethoxysilane which also serves as an antioxidant asdescribed above.

Defoaming agents, leveling agents, surface active agents, and surfacemodifiers to be used are preferably fluorine-containing compounds.

In addition to the above-described thiol-containing compounds andhindered phenol compounds, phosphorus-containing compounds anddisulfide-containing compounds are also useful as antioxidants.

Useful flame retardants include bromine-containing flame retardants,zinc compounds, antimony compounds, phosphorus compounds, andcombinations thereof. Examples of the bromine-containing flameretardants are decabromodiphenyl oxide, hexabromobenzene,hexabromocyclododecane,dodecachloropentacyclooctadeca-7,15-diene,tetrabromobisphenol A,tribromophenol, tetrabromophthalic anhydride, dibromoneopentyl glycol,and 2-(2,4,6-tribromophenoxy)ethyl (meth)acrylate. Examples of the zinccompounds are zinc borate compounds (e.g., 3ZnO₂, 2B₂O₃.3H₂O,2ZnO.3B₂O₃.3.5H₂O), zinc molybdate compounds (e.g., ZnO.ZnMoO₄,CaO.ZnMoO₄), Zn₃(PO₄)₂.4H₂O, ZnO-MgO complex calcined materials, ZnO,and ZnCO₃. Examples of the antimony compounds include antimony trioxide.

For the purpose of plasticizing the curing composition or controllingthe refractive index of the resulting cladding, non-polymerizablefluorine compounds; fluorinated alcohols, e.g.,HO(CH₂)_(r)C_(s)F_(2s+1), wherein r is an integer of from 1 to 4, and sis an integer of from 1 to 20; fluorinated carboxylic acids, e.g.,HOOC(CH₂)_(t-)C_(u)F_(2u+1), wherein t is 0 or an integer of from 1 to4, and u is an integer of from 1 to 20; fluorinated polyethers generallycalled fluorine oils; and so-called fluorine-containing inert liquids,e.g., N(C₄F₉)₃, perfluorodecalin, C₈F₁₇OC₄F₉, and C₉F₂₀, can also beadded to the curing composition.

The curing composition according to the present invention can be appliedto an optical fiber base, especially an optical fiber core, by coatingor impregnation and then irradiated with an active energy ray, e.g.,light, electron beam, or radiation, to undergo polymerization curing toform a desired coating layer or cladding layer. In some cases, heat maybe used as a curing energy source either alone or in combination withthe above-mentioned active energy ray.

Where light, such as ultraviolet light, is used as an active energy ray,photopolymerization initiators known in the art can be used as acatalyst. Examples of suitable photopolymerization initiators are (d-1)benzophenone; (d-2) acetophenone; (d-3) benzoin; (d-4) benzoin ethylether; (d-5) benzoin isobutyl ether; (d-6) benzyl methyl ketal; (d-7)azobisisobutyronitrile; (d-8) hydroxycyclohexyl phenyl ketone; and (d-9)2-hydroxy-2-methyl-1-phenylpropan-1-one. If desired, polymerization canbe accelerated by addition of photosensitizers, such as amine compoundsand phosphorus compounds.

The photopolymerization initiator is preferably used in an amount offrom 0.01 to 10% by weight, and more preferably from 0.1 to 7% byweight, based on the total weight of the curing composition. Wherepolymerization curing is effected with electron rays or radiation, anyinitiator is not particularly needed.

Where heat is utilized as a polymerization initiator, polymerizationcuring can be carried out in the presence or absence of a polymerizationinitiator, e.g., azobisisobutyronitrile, benzoyl peroxide, and methylethyl ketone peroxide-cobalt naphthenate, at a temperature e.g., of from80° to 200° C.

Polymerization curing with any of ultraviolet beam, electron rays, andradiation is preferred as compared with heat curing from the standpointof workability, productivity and economy in the production of opticalfibers and performance characteristics of the resulting optical fibers.In particular, ultraviolet curing is the most convenient and economical.

If desired, a solvent may be added to the curing composition for thepurpose of controlling viscosity, coating properties, and coating filmthickness. Solvents to be used are not particularly limited as far asthey have no adverse influences on the polymerization reaction. Examplesof suitable solvents include alcohols, e.g., methanol, ethanol, andisopropyl alcohol; ketones, e.g., acetone, methyl ethyl ketone, andmethyl isobutyl ketone; esters, e.g., methyl acetate, ethyl acetate, andbutyl acetate; chlorinated hydrocarbons, e.g., chloroform,dichloroethane, and carbon tetrachloride; and low-boiling organicsolvents, e.g., benzotrifluoride, chlorobenzotrifluoride, m-xylenehexafluoride, tetrachlorodifluoroethane,1,1,2-trichloro-1,2,3-trifluoroethane, and trichloromonofluoromethane.The solvent, if used, must be removed from the coated layer before thecommencement of polymerization curing at room temperature or, ifdesired, under heating or under reduced pressure. In cases when thesolvent is removed by heating, the heating temperature should be socontrolled as not to induce thermal polymerization of the monomers, etc.

The curing composition can be coated on an optical fiber base, i.e., anoptical fiber core or a core/cladding optical fiber, by various knowntechniques, such as coating by means of a brush, an applicator, a barcoater, a roller brush, or a roll coater; spray coating by means of anairless spray coater; flow coating by means of a shower coater or acurtain coater; dip coating; and casting. An appropriate coatingtechnique should be selected according to the material, shape or use ofthe base.

For the formation of a cladding or a coat on an optical fiber core or acore/cladding optical fiber, known coating and curing techniques asdescribed in West German Patent Publication No. 2,459,320,JP-A-53-139545, and U.S. Pat. No. 4,125,644 can be employed. Forexample, an optical fiber base is threaded through an extrusion-coatingdie, and the curing composition is continuously extrusion-coated on thebase. After removal of a solvent, if any, an active energy ray isirradiated onto the coating to form a cladding or a coat.

Any conventional active energy ray source for polymerization curing canbe used, for example, germicidal lamps, fluorescent sunlamps, carbon arclamps, xenon lamps, high-pressure mercury lamps for copying, middle- orhigh-pressure mercury lamps, ultrahigh-pressure mercury lamps,electrodeless discharge tubes, metal halide lamps, and natural sunlightfor ultraviolet rays; and scanning type or curtain type electronaccelerators for electron rays. Where a coating film having a thicknessof 5 μm or less is cured with ultraviolet rays, ultraviolet irradiationis preferably conducted in an inert gas atmosphere, e.g., nitrogen gas,for ensuring polymerization efficiency.

Optical fiber cores which can be coated with the curing composition ofthe present invention include those made of inorganic materials such asquartz, silica, and glass; and those made of plastics such as polymethylmethacrylate, deuterated polymethyl methacrylate, polystyrene, andpolycarbonate. Taking the characteristics of the curing composition ofthe present invention into consideration, quarts, silica, and glass areparticularly suitable materials.

The curing composition according to the present invention is applicableas not only a cladding of an optical fiber core or a coat of acore/cladding optical fiber as hereinbefore described but also acladding of light waveguide sheets, adhesives for optics, electricallyinsulating materials (e.g., potting materials and sealants), and wirecoatings. Further, having a low refractive index, the curing compositionof the present invention also finds its use as a low reflecting coat ona transparent glass or plastic sheet or plate or as a sealant foroptical IC.

In addition, since the curing composition of the present invention formsa cured film excellent in scratch resistance, oil resistance,smoothness, water- and oil-repellency, water resistance,moistureproofness, rustproofness, stainproofness, release properties,and low water absorption properties, it is useful as a protective coatof various materials and substrates.

For example, the curing composition is suitable as a protective coat onnon-magnetic metals, e.g., copper, aluminum and zinc; a protective coaton plastics, e.g., polyesters (e.g., polyethylene terephthalate,polyethylene-2,6-naphthalate), polyolefins (e.g., polypropylene),cellulose derivatives (e.g., cellulose acetate), and polycarbonate; and,in some cases, as a protective coat on a magnetic layer of magnetictapes or discs, including a ferromagnetic alloy film (comprising iron,cobalt and/or nickel as major components and aluminum, silicon,chromium, manganese, molybdenum, titanium, various heavy meals, or rareearth metals as minor components) deposited on glass, paper, wood,fibrous materials or ceramics (porcelain and earthenware) and a magneticlayer comprising iron, cobalt and chromium, deposited on a plastic film(e.g., a polyester film) in the presence of a trace amount of oxygen;and also as a surface or back surface treating agent for magneticrecording media, e.g., magnetic tape and floppy discs, which areparticularly required to have lubricity.

On the other hand, since the curing composition of the present inventionis capable of forming a transparent, smooth, and thin film on a glasssurface, it is also useful in applications requiring oil resistance andwiping resistance as an oil strain inhibitor or an oil penetrationinhibitor for various optical instruments.

Further, the curing composition of the present invention is suitable asa protective film of solar cells which particularly requiremoistureproofness or as a protective coat of optical fibers, opticalfiber cables, optical discs, and optomagnetic discs. Furthermore, theexcellent scratch resistance, stainproofness and moisture resistance ofthe composition can be taken advantage of for use in surface protectionof medical tools or equipment, surface protection of teeth or artificialteeth, filling of teeth, or molding of artificial teeth.

The curing composition of the present invention is applicable to variousmolded products or as hard coating agents for films, sheets, etc., sincethe coated film is excellent in scratch resistance.

The curing composition of the present invention can be compounded withpigments and dispersing agents to provide stainproof and non-tackycoatings or inks applicable to the bottom of ships.

The present invention is now illustrated in greater detail withreference to Examples, but it should be understood that the presentinvention is not deemed to be limited thereto. All the percents, parts,and ratios are by weight unless otherwise indicated.

EXAMPLES 1 TO 10 AND COMPARATIVE EXAMPLES 1 TO 3

Curing compositions of the present invention and comparativecompositions were prepared according to the formulation shown in Table1.

An optical fiber core having an outer diameter of 200 μm obtained bymelt spinning of synthetic quartz at a drawing speed of 60 m/min wasthreaded through an extrusion-coating die, and each curing compositionprepared was continuously coated thereon at the die temperature of 25°C. and cured in a nitrogen atmosphere by means of two high-pressuremercury lamps (output: 120 W/cm) to obtain a PCF having a 15 μm thickcladding.

Physical properties of the curing composition and transmission loss ofthe resulting PCF were determined according to the following testmethods. The results obtained are shown in Table 1.

1) Transparency before Curing

Transparency of a curing composition was evaluated with eyes.

2) Transparency after Curing

A curing composition was cast on a 1 mm deep glass-made tray, and a 1 mmthick quartz plate was put thereon taking care not to incorporate airbubbles. The cast composition was cured by irradiation using ahigh-pressure mercury lamp of 120 W/cm, and transparency of theresulting cured resin plate was observed with eyes.

3) Refractive Index

A refractive index of the 1 mm thick cured resin plate as prepared in(2) above with an Abbe refractometer.

4) Transmission Loss (Initial)

Transmission loss was measured at a wavelength of 850 nm according to acut-back method.

5) Transmission Loss after Exposure to Heat

After the PCF was preserved at 130° C. for 1000 hours, the transmissionloss was measured in the same manner as described above.

6) Transmission Loss after Exposure to Moisture

After the PCF was preserved at 70° C. and 98% RH for 500 hours, thetransmission loss was measured in the same manner as described above.

TABLE 1 Refractive Transmission Loss (dB/km) Transparency Index ShoreAfter After Example Curing Composition Before After After Hard- ExposureExposure No. (part) Curing Curing Curing ness Initial to Heat toMoisture Example 1 a-1 68.0 trans- trans- 1.403 D76 5.4 5.8 5.9 b-11 7.5parent parent c-15 (A*) 24.0 d-9 0.5 MPTMS** 1.4 Example 2 a-1 56.6trans- trans- 1.414 D75 5.5 5.9 5.9 b-11 18.9 parent parent c-15 (A)24.0 d-9 0.5 MPTMS 1.4 Comparative a-1 51.3 trans- slightly 1.418 D689.6 36.2 49.9 Example 1 b-11 24.2 parent turbid c-15 (A) 24.0 d-9 0.5MPTMS 1.4 Comparative n-1 68.0 opaque whitened unmeasure-D-43 >100 >300 >300 Example 2 n-7 7.5 able c-15 (A) 24.0 d-9 0.5 MPTMS1.4 Comparative a-1 75.5 opaque whitened unmeasure- D45 >100 >300 >300Example 3 c-15 (A) 24.0 d-9 0.5 MPTMS 1.3 Example 3 a-1 66.2 trans-trans- 1.408 D74 5.6 6.5 6.4 b-8 9.3 parent parent c-15 (A) 24.0 d-9 0.5MAPTMS*** 0.5 acrylic 0.1 acid Example 4 a-1 66.2 trans- trans- 1.408D74 5.5 5.7 5.8 b-8 9.3 parent parent c-15 (A) 24.0 d-9 0.5 MPTMS 1.3Example 5 a-1 70.0 trans- trans- 1.400 D75 5.7 6.5 6.6 b-1 5.0 parentparent c-15 (A) 24.0 d-9 0.5 octyl thio- 0.5 glycolate MPATMS 0.5Example 6 a-1 72.5 trans- trans- 1.401 D77 5.4 5.7 5.8 b-8 3.0 parentparent c-15 (A) 22.0 c-9 (A) 2.0 d-9 0.5 MPTMS 1.4 Example 7 a-1 40.9trans- trans- 1.437 D79 5.5 5.9 6.1 b-3 13.6 parent parent c-15 (A) 45.0d-9 0.5 MAPTMS 0.7 TP**** 0.5 Example 8 a-7 76.8 trans- trans- 1.397 D685.4 5.7 5.7 b-11 3.2 parent parent c-15 (A) 19.5 d-9 0.5 MFTMS 1.2Example 9 a-13 68.0 trans- trans- 1.402 D75 5.5 6.2 6.2 b-11 7.5 parentparent c-15 (A) 24.0 d-9 0.5 MFTMS 1.2 Example 10 a-1 68.0 trans- trans-1.403 D75 5.5 6.3 6.4 b-11 7.5 parent parent c-15 (A) 24.0 d-9 0.5MAPTMS 1.4 Note: *Acrylate compound **γ-Mercaptopropyltrimethoxysilane***γ-Methacryloxypropyltrimethoxysilane****2,2-Thio-diethylenebis(3-(3,5-di-i-butyl-4-hydroxyphenyl)propionase

EXAMPLE 11

Curing compositions having the following formulation were prepared usingeach of the fluorinated (meth)acrylates (A) and fluorinated(meth)acrylates (B) shown in Table 2. A Shore hardness after curing andtransparency before and after curing were examined. The results obtainedare shown in Table 2.

Formulation Fluorinated (meth)acrylate (A) 63.6% Fluorinated(meth)acrylate (B) 15.9% c-15 (A) 20.0% d-9 0.5%γ-Mercaptopropyltrimethoxysilane 1.2%

The symbol “G” in Table 2 means satisfactory transparency:- the left oneindicates transparency before curing, and the right one after curing.

TABLE 2 Fluor- inated (Meth)- acry- late Fluorinated (Meth)acrylate (A)(B) a-1 a-2 a-5 a-6 a-7 a-8 a-9 a-12 a-13 b-1  D75 D75 D77 D70 D73 D73D66 D76 D79 G/G G/G G/G G/G G/G G/G G/G G/G G/G b-2  D76 D73 D76 D69 D70D70 D65 D77 D79 G/G G/G G/G G/G G/G G/G G/G G/G G/G b-3  D74 D72 D77 D65D72 D72 D66 D78 D77 G/G G/G G/G G/G G/G G/G G/G G/G G/G b-4  D70 D72 D70D68 D70 D72 D67 D76 D78 G/G G/G G/G G/G G/G G/G G/G G/G G/G b-5  D76 D74D76 D69 D70 D73 D65 D75 D79 G/G G/G G/G G/G G/G G/G G/G G/G G/G b-6  D77D73 D78 D70 D71 D74 D64 D77 D79 G/G G/G G/G G/G G/G G/G G/G G/G G/G b-7 D77 D74 D76 D65 D73 D73 D64 D76 D77 G/G G/G G/G G/G G/G G/G G/G G/G G/Gb-8  D79 D80 D79 D69 D78 D76 D66 D80 D77 G/G G/G G/G G/G G/G G/G G/G G/GG/G b-9  D78 D80 D75 D65 D76 D76 D67 D78 D76 G/G G/G G/G G/G G/G G/G G/GG/G G/G b-10 D77 D76 D72 D66 D76 D75 D66 D76 D77 G/G G/G G/G G/G G/G G/GG/G G/G G/G b-11 D78 D78 D77 D67 D76 D74 D64 D77 D78 G/G G/G G/G G/G G/GG/G G/G G/G G/G b-12 D77 D77 D74 D66 D77 D77 D64 D76 d78 G/G G/G G/G G/GG/G G/G G/G G/G G/G b-13 D78 D79 D76 D67 D75 D73 D65 D78 D77 G/G G/G G/GG/G G/G G/G G/G G/G G/G b-14 D78 D64 D77 D65 D74 D75 D65 D77 D76 G/G G/GG/G G/G G/G G/G G/G G/G G/G

When the whole or half of c-15(A) was replaced with c-9(A), each of thecompositions had satisfactory transparency both before and after curing.

EXAMPLE 12

Curing compositions (5×5×5 mm) having the following formulation wereprepared using each of the fluorinated (meth)acrylates (A) andfluorinated (meth)acrylates (B) shown in Tables 3 and 4.

Formulation Fluorinated (meth)acrylate (A) 63.6% Fluorinated(meth)acrylate (B) 15.9% c-15 (A) 20.0% d-9 0.5%γ-Mercaptopropyltrimethoxysilane 1.2%

For an immersion test, these curing compositions were immersed inacetone or ethyl acetate at 23° C., and then the weight change (wt %)after immersion for 48 hours (i.e., swelling degree) was measured. Theresults obtained are shown in Tables 3 and 4.

TABLE 3 Immersion in Acetone Fluorinated Fluorinated (Meth)acrylate (A)(Meth)acrylate (B) a-1 a-7 b-8  +1.3 +1.9 b-9  +1.2 +1.7 b-10 +1.5 +1.9b-11 +4.7 +5.3 b-12 +4.5 +5.2

TABLE 4 Immersion in Ethyl Acetate Fluorinated Fluorinated(Meth)acrylate (A) (Meth)acrylate (B) a-1 a-7 b-8  +3.7 +4.6 b-9  +3.5+4.4 b-10 +3.9 +4.7 b-11 +6.4 +7.8 b-12 +6.4 +7.6

As is clear from Tables 3 and 4, the cured resin of the compositionusing a combination of a-1 and b-8, a combination of a-1 and b-9, or acombination of a-1 and b-10 exhibited far more excellent solventresistance than that of the composition using a combination of a-1 andb-11 or a combination of a-1 and b-12. Further, the cured resin of thecomposition using a combination of a-7 and b-8, a combination of a-7 andb-9, or a combination of a-7 and b-10 exhibited far more excellentsolvent resistance than that of the composition using a combination ofa-7 and b-11 or a combination of a-7 and b-12.

As described and demonstrated above, the curing resin compositionaccording to the present invention is excellent in transparency andhomogeneity at room temperature and is also excellent in transparencyand dynamic strength after curing. Thus, when it is used as a claddingmaterial or a coating material of optical fibers, excellent workabilityis obtained because of no need to heat as has been usual with theconventional cladding materials, whereby the problem of eccentricityfrequently accompanying heating can be minimized while providing opticalfibers excellent in mechanical strength, optical characteristics, andenvironmental resistance such as heat resistance and moistureresistance.

While the invention has been described in detail and with reference tospecific examples thereof, it will be apparent to one skilled in the artthat various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

1. A curable coating composition comprising: 1) a first monomerrepresented by formula (A)RfOCOC(R)═CH₂  (A)  wherein Rf represents a linear or branchedfluorinated alkyl group having not less that than 6 carbon atoms, ahydroxyl substituted fluorinated alkyl having not less that than 6carbon atoms, a fluorinated sulfonamide having not less that than 6carbon atoms, or a fluorinated amide having not less that than 6 carbonatoms, and R represents H. , F, or C₁₋₁₀ fluorinated alkyl; 2) a secondmonomer represented by formula (B)Rf′OCOC(R′)═CH₂  (B)  wherein Rf′ represents a linear or branched C₁₋₅fluorinated alkyl and R′ represents —H, —F, or —CH₃; and 3) at least onepolyfunctional methacrylic curable monomer, wherein the weight ratio ofthe first monomer to the second monomer is from 75:25 to 99:1.
 2. Acurable coating composition as defined in claim 1, wherein the firstmonomer is a member of the group consisting of C₈F₁₇CH₂CH₂OCOC(R)═CH₂and C₆F₁₃CH₂CH₂OCOC(R)═CH₂ and R represents H, F, or C₁₋₁₀ fluorinatedalkyl.
 3. A curable coating composition as defined in claim 1, whereinRf′ is at least one of a branched C₁₋₅ fluorinated alkyl or a linearC₁₋₅ fluorinated alkyl, each having a fluorohydrocarbon end group.
 4. Acurable coating composition as defined in claim 1, wherein the secondmonomer is a member of the group consisting of H(CF₂CF₂)₂CH₂OCOC(R′)═CH₂and (CF₃)₂CHOCOC(R′)═CH₂.
 5. A curable coating composition as defined inclaim 1, wherein the polyfunctional curable monomer is present in anamount of 1 to 50% by weight compared to the total weight of the curablecomposition.
 6. A curable composition as claimed in claim 1, whereinsaid polyfunctional curing monomer (3) is (CH₂═C(R)COOCH₂)₃CC₂H₅,wherein R represents a hydrogen atom, a methyl group, or a fluorineatom.
 7. A curable composition as claimed in claim 1, wherein saidpolyfunctional curing monomer (3) is trimethylolpropane triacrylate. 8.A curable composition as claimed in claim 1, wherein said compositioncontains a thiol-containing compound.
 9. A curable composition asclaimed in claim 8, wherein said thiol-containing compound isγ-mercaptopropyltrimethoxysilane.
 10. A process for preparing atransparent cured coating on a substrate, comprising the steps of: (A)applying on a substrate a coating of a curable resin compositioncomprising: 1) a first monomer represented by formula (A)RfOCOC(R)═CH₂  (A)  wherein Rf represents a linear or branchedfluorinated alkyl group having not less than 6 carbon atoms, a hydroxylsubstituted fluorinated alkyl having not less than 6 carbon atoms, afluorinated sulfonamide having not less than 6 carbon atoms, or afluorinated amide having not less than 6 carbon atoms, and R representsH, F, or C₁₋₁₀ fluorinated alkyl; 2) a second monomer represented byformula (B)Rf′OCOC(R′)═CH₂  (B)  wherein Rf′ represents a linear or branched C₁₋₅fluorinated alkyl and R′ represents —H, —F, or —CH₃; and 3) at least onepolyfunctional methacrylic curable monomer, wherein the weight ratio ofthe first monomer to the second monomer is from 75:25 to 99:1; and (B)curing the coating by applying active energy radiation, heat, or acombination of active energy radiation and heat.
 11. A process as inclaim 10, wherein the first monomer is a member selected from the groupconsisting of C₈F₁₇CH₂CH₂OCOC(R)═CH₂ and C_(6F) ₁₃CH₂CH₂OCOC(R)═CH₂ andR represents H, F, or C₁₋₁₀ fluorinated alkyl.
 12. A process as in claim10, wherein Rf′ is at least one member selected from the groupconsisting of a branched C₁₋₅ fluorinated alkyl and a linear C₁₋₅fluorinated alkyl, each having a fluorohydrocarbon group.
 13. A processas in claim 10, wherein the second monomer is one member selected fromthe group consisting of H(CF₂CF₂)₂CH₂OCOC(R′)═CH₂ and(CF₃)₂CHOCOC(R′)═CH_(2.)
 14. A process as in claim 10, wherein thepolyfunctional curable monomer is present in an amount of 1 to 50% byweight compared to the total weight of the curable composition.
 15. Aprocess as in claim 10, wherein said polyfunctional curing monomer (3)is (CH₂═C(R)COOCH₂)₃ CC₂H₅, wherein R represents a hydrogen atom, amethyl group, or a fluorine atom.
 16. A process as in claim 10, whereinsaid polyfunctional curing monomer (3) is trimethylolpropanetriacrylate.
 17. A process as in claim 10, wherein said compositioncontains a thiol-containing compound.
 18. A process as in claim 17,wherein said thiol-containing compound isγ-mercaptopropyltrimethoxysilane.